The present invention relates generally to an internal combustion steam engine that operates with an alcohol fuel and, in particular, to an alcohol-water fuel system for supplying a vaporizing fuel to the engine. Upon combustion, superheated steam is generated within the cylinders to produce an elevated pressure and temperature. More specifically, the present invention pertains to a unique combination of internal combustion and external burner steam technologies particularly adapted for the recirculation of heat energy to produce a highly efficient engine adapted for automotive and other uses.
Conventional gasoline engines operate on what is known as the OTTO cycle wherein a carbureted mixture of fuel and air is ignited following compression in the well known manner and, thereafter, expelled to the surroundings through an exhaust manifold and muffler system. Such engines, however, exhibit substantial losses of heat and other energy which, in turn, results in poor fuel to mechanical work energy conversion. First, the burning gases produce a mean effective pressure in the cylinder of about 100-200 psi but at an extremely elevated temperature of typically 3000.degree. F. This excessive heat, which is generally dissipated through an engine radiator to avoid cylinder and piston destruction, accounts for an approximate 35 percent loss in the BTU energy of unburned gasoline fuel.
Further, it is known that proper stoichiometric mixtures for complete fuel burning do not ignite readily and, therefore, excessive fuel (i.e. rich mixture) is generally provided. This, in turn, results in partial or unburned carbon exhaust products contributing to environmental pollution and further losses in efficiency. As an alternative, conventional fuel injection systems may be employed to directly inject fuel droplets into the airstream. Although more efficient than conventional carburetors, the injection of relatively large droplets, typically 0.050 inches in diameter, still results in incomplete combustion.
In addition to the above described unburned fuel and coolant energy losses, the exhaust gases are quite hot, often in excess of 1500.degree. F., thereby adding further to the heat energy loss. Indeed, it is common to see exhaust manifolds heated to glowing, and flames emitted from the exhaust pipe are not uncommon. In total, these exhaust related losses account for another 35 percent of the total gasoline fuel energy. Deducting yet another 10 percent for frictional losses, the overall efficiency of a typical internal combustion gasoline engine is in the order of about 20 percent.
In sharp contrast to the elevated operating temperatures of gasoline fueled internal combustion engines, a typical external combustion steam engine operates at temperatures between about 440.degree. F. and 470.degree. F. corresponding to steam pressures between about 400 psi and 500 psi. Thus, a conventional external combustion steam engine produces the requisite cylinder pressure but at a greatly reduced operating temperature which, in turn, significantly lessens engine cooling and exhaust heat losses.
Conventional external combustion steam engines, however, have several dissadvantages which render them unsuitable for use in modern automobiles. First, a relatively bulky boiler is required to generate the steam. In addition, significant time is required to heat the boiler to operating pressures which delays productive use of the engine upon initial start-up and, during low load periods, renders the system relatively more inefficient.
Conventional external combustion steam engines are, in any event, rather inefficient. These engines, which operate on the RANKINE cycle, require the burning of fuel to heat and vaporize water contained within a boiler. The resulting steam passes through necessary piping and controls and, in turn, is admitted to engine cylinder. Assuming that the boiler water is initially at 32.degree. F., 180 BTU per pound must be added to raise the water to the 212.degree. F. boiling point and an additional 1030 BTU to convert the water to the steam phase at 500 psi. Assuming, further, that a typical steam engine exhausts the steam at as little as 20 psi, an overall engine efficiency of 4 percent results. Even this low efficiency figure is optimistic as other losses including boiler efficiency were not considered.
The present internal combustion steam engine, by contrast, represents a highly efficient combination of steam and internal combustion technologies particularly suited to the reclamation of otherwise lost heat energies. First, the energy in the engine cooling system is recycled to vaporize the water-alcohol fuel mixture. This vaporized fuel burns more rapidly thereby producing the maximum pressure in the cylinder and the highest mean effective pressure. The water enters the cylinder as a vapor with an enthalpy already at 1150 BTU per pound requiring only an additional 50 BTU to raise its pressure, as in the steam engine example above, to 500 psi. Assuming, again, an exhaust pressure of 20 psi and substantially complete recirculation of the coolant energy (actually, a few percent recirculation loss is typical), a thermal efficiency of about 88 percent results.
Further, since substantially all the fuel of the present invention is burned, there is correspondingly little lost fuel energy and minimal environmental pollution. To further improve the efficiency of the present engine, the exhaust gases may advantageously be recirculated to preheat the carburetor inlet air to approximately 500.degree. F. thereby further reducing the heat which must be subsequently added or generated in the steam combustion cylinder cycle. In this manner, the exhaust losses are reduced to about 15 percent. Considering frictional losses, an overall efficiency of slightly more than 50 percent may be achieved. This is about three times the efficiency of a conventional gasoline internal combustion engine, about twice that of a diesel, and over ten times as efficient as a steam engine.
A further advantage of the present engine is that it may be operated with many differing fuels including most alcohols. This includes a variety of hydroxyl derivatives of hydrocarbons such as methanol, ethanol, isopropanol, tertiary butanol and mixtures thereof with water. The preferred fuel is ethanol which can advantageously be made inexpensively from organic waste. In addition, ethanol will support combustion when mixed with water even at low concentrations. This heat of combustion turns the water into, or superheats, the steam.
Internal combustion engines operated with alcohol or a blended gasoline-alcohol mixture are well known. Such blending, however, lowers the boiling point of the gasoline and thereby causes vapor lock in the fuel pump at a lower temperature than would be the case with pure gasoline. In addition, the introduction of water to a blended gasoline-alcohol fuel mixture causes the mixture to separate into its constituent phases. Since the resultant fuel supplied to the carburetor is not of constant composition and does not correspond to the composition to which the carburetor was initially adjusted, the engine malfunctions.